Charging batteries in a car for Sony EX3

I will be shooting a little doco in a couple of weeks and I am researching how I could charge my batteries. I will be out in the field for several days and the only power source I have os the car power outlet (cigarette lighter).

Is there a charger out there which I could use to charge my batteries through the car power outlet? Or should I buy an dapter which comes first in the line?

Maybe one of you has dealt with this problem in the past and can give me some advice.

I charge my still camera stuff and power my netbook using a cheap inverter. Lower current ones plug into your 12v accy/lighter and deliver plenty to drive a battery charger.

Using an EX3 I did a long interval recording of a 13 million pound dragline crane "walking" across a four lane highway on a temporary man-made cross road in -40F (well, that's -40C too) at about a tenth of a mile per hour. I parked the truck sideways in the median, rolled down the back window, and shot from the truck due to wind and cold. I ran that EX3 on the inverter for the entire time, a couple of hours at least, while I ran around and shot the run-n-gun stuff with the EX1 outside. Coldest shoot I ever had. My Canon still camera batteries froze up frequently but the Sony batteries had no issues.

For shooting aurora borealis I even bring a 100' extension cord reel so I can drive a set of Logitech speakers to provide mood music. :) This is all from a relatively small inverter; if you wanted to drive a lot of equipment, you could always get a higher wattage model that connects directly to the vehicle battery.